One problem related to transmission noise has been reported for the 2011 Ford Flex. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2011 Ford Flex based on all problems reported for the 2011 Flex.
Ptu failure - I have had my Flex since 2012. I have never had an issue with anything in that vehicle. I am in the military, and I travel a lot. I have that oil changed and tires rotated religiously. Fluids are always topped off. I just turned over 120,000 miles on my 2011 Flex, 85 percent of those miles were highway. My Flex started hesitating, occasionally. An occasional jerk into gear. Then started making metal-grinding noises, then sputtering. This happened over a 3 month period. I find out my ptu is shot, of course I am over the mileage for the warranty - shocker. So I have to put out 1888. 00 to repair this. I started doing some research on Ford, and Flexes and was shocked to see that the transmission repair facility was very aware of this common issue, in their edge, Flex and other full wheel or all wheel drive vehicles. And still no recall.